Conventionally, regional heat supply systems have been practically applied, wherein heat medium such as cooled water, warm water, and vapor, which are intensively produced in one or several heat supply facilities (regional heating and cooling plants), are supplied to a plurality of buildings by use of regional pipes. For example, when a heat supply facility A supplies the heat medium to a region A, the heat supply systems of this type is designed and operated in such a manner as to maintain a difference between the temperature of the heat medium supplied to the buildings in the region A and the temperature of the heat medium utilized for air-conditioning in the buildings and the like and returned to the heat supply facility A in a predetermined range (when the difference in temperatures is out of the predetermined range, the heat supply facility A cannot supply the heat medium having a predetermined temperature to the buildings in the region A). Accordingly, this makes it possible to stably supply heat energy required for each building from the heat supply facility A to each building in the region A.
However, with this constitution, even when the heat supply facility A, which supplies the heat medium to the region A, and a heat supply facility B, which supplies the heat medium to a region B are adjacent to each other, the heat supply in the regions A and B cannot be efficiently carried out by integrally operating the heat supply facility A and the heat supply facility B. In general, the heat demands in the region A and the region B are not equal, and as a result, this is attributed to a difference between the temperature of the heat medium supplied from the heat supply facility A and the temperature of the heat medium supplied from the heat supply facility B. When the temperatures of the heat media supplied from each heat supply facility are different, and the regional pipes of respective regional heat supply systems are simply connected to each other, the heat media having different temperatures are mixed, which causes fluctuation in the temperatures of the heat media at the connection point. Then, it becomes difficult to maintain a difference between the temperature of the heat medium supplied from the heat supply facility and the temperature of the heat medium returned to the heat supply facility in a predetermined range, and as a result, the heat energy required for the buildings in each region cannot be supplied.
In order to avoid the problem of mixture of the heat media, for example, Patent Literature 1 discloses constitution in which the regional heat supply system, which supplies the heat medium to the region A, and the regional heat supply system, which supplies the heat medium to the region B, are connected via a heat storage tank. With this constitution, for example, when the temperature of the heat medium supplied to the region B is higher than the temperature of the heat medium supplied to the region A, the heat medium flowing through the regional pipes in the region A are introduced to the heat storage tank. In the heat storage tank, the temperature of the heat medium is raised by use of the heat energy of the heat medium flowing through a return pipe, and the heat medium whose temperature has been raised, is supplied to the regional pipes in the region B. Also, in order to avoid the problem of the mixture of the heat media, Patent Literature 2 discloses constitution in which a plurality of return pipes are provided, thereby changing the return pipes that are used in accordance with the temperature of the heat medium.
On the other hand, Non-Patent Literature 1 proposes “Best Effort Type Heat Accommodation Network” in which a heat source is provided in each building or each house, and the heat is interchanged between houses and the buildings in the neighborhood, not the type of supplying the heat medium from a specific heat supply facility to the buildings in a region as described above.